The development of next-generation aqueous supercapatteries with high energy and long life remains impeded by traditional redox-active electrode materials, which exhibit slow redox kinetics and low conductivity. In this work, a rationally designed Ni-Co3(PO4)2.8H2O@NiCoSe2 (NCP@NCSe) heterostructure electrode is reported for energy storage applications. As a positive electrode for supercapacitors, the heterostructure offers synergistic interfacial charge-storage mechanisms and enhanced structural durability. The assembled NCP@NCSe||AC (Activated Carbon) device exhibits an outstanding specific capacity of 251.7 mAh g−1, a high energy density of 68.5 Wh kg−1, and a reasonable power density of 272.2 W kg−1 at a current density of 1 mA g−1. The heterostructured interface between different materials exposes inaccessible Co redox sites, thereby increasing charge-storage efficiency. Hence, the supercapattery delivers a significant energy density with a reasonable power density and, at the same time, exhibits excellent cycling durability with 88% capacity retention after 5000 cycles. The collective enhancements clearly indicate that heterostructure engineering is an effective method for getting a well-balanced trade-off between energy and power density in aqueous supercapatteries.